Targeting focal adhesion kinase with dominant-negative FRNK or Hsp90 inhibitor 17-DMAG suppresses tumor growth and metastasis of SiHa cervical xenografts

Targeting Ras signaling excitability in cancer cells through combined inhibition of FAK and PI3K

The Ras/PI3K/ERK signaling network is frequently mutated in various human cancers including cervical cancer and pancreatic cancer. Previous studies showed that the Ras/PI3K/ERK signaling network displays features of excitable systems including propagation of activity waves, all-or-none responses, and refractoriness. Oncogenic mutations lead to enhanced excitability of the network. A positive feedback loop between Ras, PI3K, the cytoskeleton, and FAK was identified as a driver of excitability. In this study, we investigated the effectiveness of targeting signaling excitability by inhibiting both FAK and PI3K in cervical and pancreatic cancer cells. We found that the combination of FAK and PI3K inhibitors synergistically suppressed the growth of select cervical and pancreatic cancer cell lines through increased apoptosis and decreased mitosis. In particular, FAK inhibition caused downregulation of PI3K and ERK signaling in cervical cancer but not pancreatic cancer cells. Interestingly, PI3K inhibitors activated multiple receptor tyrosine kinases (RTKs), including insulin receptor and IGF-1R in cervical cancer cells, as well as EGFR, Her2, Her3, Axl, and EphA2 in pancreatic cancer cells. Our results highlight the potential of combining FAK and PI3K inhibition for treating cervical and pancreatic cancer, although appropriate biomarkers for drug sensitivity are needed, and concurrent targeting of RTKs may be required for resistant cells.

Autophagy, molecular chaperones, and unfolded protein response as promoters of tumor recurrence

Tumor recurrence is a paradoxical function of a machinery, whereby a small proportion of the cancer cell population enters a resistant, dormant state, persists long-term in this condition, and then transitions to proliferation. The dormant phenotype is typical of cancer stem cells, tumor-initiating cells, disseminated tumor cells, and drug-tolerant persisters, which all demonstrate similar or even equivalent properties. Cancer cell dormancy and its conversion to repopulation are regulated by several protein signaling systems that inhibit or induce cell proliferation and provide optimal interrelations between cancer cells and their special niche; these systems act in close connection with tumor microenvironment and immune response mechanisms. During dormancy and reawakening periods, cell proteostasis machineries, autophagy, molecular chaperones, and the unfolded protein response are recruited to protect refractory tumor cells from a wide variety of stressors and therapeutic insults. Proteostasis mechanisms functionally or even physically interfere with the main regulators of tumor relapse, and the significance of these interactions and implications in the tumor recurrence phases are discussed in this review.

FAK displacement from focal adhesions: a promising strategy to target processes implicated in cancer progression and metastasis

BACKGROUND

Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase that is overexpressed or activated in several advanced-stage solid cancers. It is known to play both kinase-dependent and -independent roles in promoting tumor progression and metastasis. Numerous inhibitors, targeting either the enzymatic or scaffolding activities of FAK have been generated, with varying degree of success. Here, we describe a novel approach to site-specifically target both kinase-dependent and -independent FAK functions at focal adhesions (FAs), the primary sites at which the kinase exerts its activity.

METHODS

We took advantage of the well-characterized interactions between the paxillin LD motifs and the FAK FAT domain and generated a polypeptide (LD2-LD3-LD4) expected to compete with interactions with paxillin. Co-immunoprecipitation experiments were performed to examine the interaction between the LD2-LD3-LD4 polypeptide and FAK. The effects of LD2-LD3-LD4 in the localization and functions of FAK, as well as FA composition, were evaluated using quantitative immunofluorescence, cell fractionation, FA isolation and Western Blot analysis. Live cell imaging, as well as 2-D migration and cell invasion assays were used to examine the effects on FA turnover and tumor cell migration and invasion.

RESULTS

Expression of the LD2-LD3-LD4 polypeptide prevents FAK localization at FAs, in a controlled and dose-dependent manner, by competing with endogenous paxillin for FAK binding. Importantly, the LD2-LD3-LD4 peptide did not otherwise affect FA composition or integrin activation. LD2-LD3-LD4 inhibited FAK-dependent downstream integrin signaling and, unlike existing inhibitors, also blocked FAK's scaffolding functions. We further show that LD2-LD3-LD4 expression markedly reduces FA turnover and inhibits tumor cell migration and invasion. Finally, we show that dimers of a single motif, linked through a flexible linker of the proper size, are sufficient for the displacement of FAK from FAs and for inhibition of tumor cell migration. This work raises the possibility of using a synthetic peptide as an antimetastatic agent, given that effective displacement of FAK from FAs only requires dimers of a single LD motif linked by a short flexible linker.

CONCLUSION

In conclusion, these results suggest that FAK displacement from FAs is a promising new strategy to target critical processes implicated in cancer progression and metastasis. Video abstract.

Potential role of senescence in radiation-induced damage of the aged skeleton

Human aging-related changes are exacerbated in cases of disease and cancer, and conversely aging is a catalyst for the occurrence of disease and multimorbidity. For example, old age is the most significant risk factor for cancer and among people who suffer from cancer, >60% are above the age of 65. Oxidative stress and DNA damage, leading to genomic instability and telomere dysfunction, are prevalent in aging and radiation-induced damage and are major cellular events that lead to senescence. Human exposures from nuclear fallout, cosmic radiation and clinical radiotherapy (RT) are some common sources of irradiation that affect bone tissue. RT has been used to treat malignant tumors for over a century, but the effects of radiation damage on tumor-adjacent normal tissue has largely been overlooked. There is an increase in the percent survivorship among patients post-RT, and it is in older survivors where the deleterious synergy between aging and radiation exposure conspires to promote tissue deterioration and dysfunction which then negatively impacts their quality of life. Thus, an aging skeleton is already pre-disposed to architectural deterioration, which is further worsened by radiation-induced bone damage. Effects of senescence and the senescence associated secretory phenotype (SASP) have been implicated in age-associated bone loss, but their roles in radiation-associated bone damage are still elusive. RT is used in treatment for a variety of cancers and in different anatomical locations, the sequelae of which include long-term morbidity and lifelong discomfort. Therefore, consideration of the growing evidence that implicates the role of senescence in radiation-induced bone damage argues in favor of exploiting current senotherapeutic approaches as a possible prevention or treatment.

Targeted cancer therapy through 17-DMAG as an Hsp90 inhibitor: Overview and current state of the art

Heat shock protein 90 (Hsp90) is an evolutionary preserved molecular chaperone which mediates many cellular processes such as cell transformation, proliferation, and survival in normal and stress conditions. Hsp90 plays an important role in folding, maturation, stabilization and activation of Hsp90 client proteins which all contribute to the development, and proliferation of cancer as well as other inflammatory diseases. Functional inhibition of Hsp90 can have a massive effect on various oncogenic and inflammatory pathways, and will result in the degradation of their client proteins. This turns it into an interesting target in the treatment of different malignancies. 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG) as a semi-synthetic derivative of geldanamycin, has several advantages over 17-Allylamino-17-demethoxygeldanamycin (17-AAG) such as higher water solubility, good bioavailability, reduced metabolism, and greater anti-tumour capability. 17-DMAG binds to the Hsp90, and inhibits its function which eventually results in the degradation of Hsp90 client proteins. Here, we reviewed the pre-clinical data and clinical trial data on 17-DMAG as a single agent, in combination with other agents and loaded on nanomaterials in various cancers and inflammatory diseases.

Aberrant methylation-mediated silencing of microRNAs contributes to HPV-induced anchorage independence

Cervical cancer and a subset of anogenital and head-and-neck carcinomas are caused by high-risk types of the human papillomavirus (hrHPV). During hrHPV-induced malignant transformation keratinocytes become able to grow anchorage independently, a tumorigenic trait at least partly associated with inactivation of tumor suppressor genes. We used hrHPV-containing keratinocytes to investigate the role of DNA methylation-mediated silencing of microRNAs (miRNAs) in the acquisition of anchorage independence.

Anchorage dependent (n=11) and independent passages (n=19) of 4 hrHPV-immortalized keratinocyte cell lines were treated with 2′-deoxy-5-azacytidine (DAC). Genome-wide miRNA expression profiles before and after treatment were compared to identify miRNAs silenced by methylation. Bisulfite sequencing and methylation-specific PCR showed increased methylation of hsa-mir-129-2/-137/-935/-3663/-3665 and -4281 in anchorage independent HPV-transformed keratinocytes and cervical cancer cell lines. Mature miRNAs derived from hsa-mir-129-2/-137/-3663 and -3665 showed functional relevance as they decreased anchorage independence in cervical cancer cell lines. Cervical (pre)cancerous lesions demonstrated increased methylation of hsa-mir-129-2/-935/-3663/-3665 and -4281, underlining the clinical relevance of our findings.

In conclusion, methylation-mediated silencing of tumor suppressive miRNAs contributes to acquisition of an anchorage independent phenotype. This study further substantiates the importance of miRNAs during early stages of carcinogenesis and underlines their potential as both disease markers and therapeutic targets.

Regulation of Focal Adhesion Kinase through a Direct Interaction with an Endogenous Inhibitor

Focal adhesion kinase (FAK) plays a key role in integrin and growth factor signaling pathways. FAK-related non-kinase (FRNK) is an endogenous inhibitor of FAK that shares its primary structure with the C-terminal third of FAK. FAK S910 phosphorylation is known to regulate FAK protein-protein interactions, but the role of the equivalent site on FRNK (S217) is unknown. Here we determined that S217 is highly phosphorylated by ERK in cultured rat aortic smooth muscle cells. Blocking phosphorylation by mutation (S217A) greatly increased FRNK inhibitory potency, resulting in strong inhibition of FAK autophosphorylation at Y397 and induction of smooth muscle cell apoptosis. FRNK has been proposed to compete for FAK anchoring sites in focal adhesions, but we did not detect displacement of FAK by WT-FRNK or superinhibitory S217A-FRNK. Instead, we found FRNK interacted directly with FAK, and this interaction is markedly strengthened for the superinhibitory S217A-FRNK. The results suggest that FRNK limits growth and survival signaling pathways by binding directly to FAK in an inhibitory complex, and this inhibition is relieved by phosphorylation of FRNK at S217.

The Ig VH complementarity-determining region 3-containing Rb9 peptide, inhibits melanoma cells migration and invasion by interactions with Hsp90 and an adhesion G-protein coupled receptor

The present work aims at investigating the mechanism of action of the Rb9 peptide, which contains the V_HCDR 3 sequence of anti-sodium-dependent phosphate transport protein 2B (NaPi2B) monoclonal antibody RebMab200 and displayed antitumor properties. Short peptides corresponding to the hypervariable complementarity-determining regions (CDRs) of immunoglobulins have been associated with antimicrobial, antiviral, immunomodulatory and antitumor activities regardless of the specificity of the antibody. We have shown that the CDR derived peptide Rb9 induced substrate hyperadherence, inhibition of cell migration and matrix invasion in melanoma and other tumor cell lines. Rb9 also inhibited metastasis of murine melanoma in a syngeneic mouse model. We found that Rb9 binds to and interferes with Hsp90 chaperone activity causing attenuation of FAK-Src signaling and downregulation of active Rac1 in B16F10-Nex2 melanoma cells. The peptide also bound to an adhesion G-protein coupled receptor, triggering a concentration-dependent synthesis of cAMP and activation of PKA and VASP signaling as well as IP-3 dependent Ca²⁺ release. Hsp90 is highly expressed on the cell surface of melanoma cells, and synthetic agents that target Hsp90 are promising cancer therapeutic drugs. Based on their remarkable antitumor effects, the CDR-H3-derived peptides from RebMab200, and particularly the highly soluble and stable Rb9, are novel candidates to be further studied as potential antitumor drugs, selectively acting on cancer cell motility and invasion.

Exploring the interaction between human focal adhesion kinase and inhibitors: a molecular dynamic simulation and free energy calculations

Focal adhesion kinase is an important target for the treatment of many kinds of cancers. Inhibitors of FAK are proposed to be the anticancer agents for multiple tumors. The interaction characteristic between FAK and its inhibitors is crucial to develop new inhibitors. In the present article, we used Molecular Dynamic (MD) simulation method to explore the characteristic of interaction between FAK and three inhibitors (PHM16, TAE226, and ligand3). The MD simulation results together with MM-GB/SA calculations show that the combinations are enthalpy-driven process. Cys502 and Asp564 are both essential residues due to the hydrogen bond interactions with inhibitors, which was in good agreement with experimental data. Glu500 can form a non-classical hydrogen bond with each inhibitor. Arg426 can form electrostatic interactions with PHM16 and ligand3, while weaker with TAE226. The electronic static potential was employed, and we found that the ortho-position methoxy of TAE226 has a weaker negative charge than the meta-position one in PHM16 or ligand3. Ile428, Val436, Ala452, Val484, Leu501, Glu505, Glu506, Leu553, Gly563 Leu567, Ser568 are all crucial residues in hydrophobic interactions. The key residues in this work will be available for further inhibitor design of FAK and also give assistance to further research of cancer.

Heat shock protein 90 is involved in the regulation of HMGA2-driven growth and epithelial-to-mesenchymal transition of colorectal cancer cells

High Mobility Group AT-hook 2 (HMGA2) is a nonhistone chromatin-binding protein which acts as a transcriptional regulating factor involved in gene transcription. In particular, overexpression of HMGA2 has been demonstrated to associate with neoplastic transformation and tumor progression in Colorectal Cancer (CRC). Thus, HMGA2 is a potential therapeutic target in cancer therapy. Heat Shock Protein 90 (Hsp90) is a chaperone protein required for the stability and function for a number of proteins that promote the growth, mobility, and survival of cancer cells. Moreover, it has shown strong positive connections were observed between Hsp90 inhibitors and CRC, which indicated their potential for use in CRC treatment by using combination of data mining and experimental designs. However, little is known about the effect of Hsp90 inhibition on HMGA2 protein expression in CRC. In this study, we tested the hypothesis that Hsp90 may regulate HMGA2 expression and investigated the relationship between Hsp90 and HMGA2 signaling. The use of the second-generation Hsp90 inhibitor, NVP-AUY922, considerably knocked down HMGA2 expression, and the effects of Hsp90 and HMGA2 knockdown were similar. In addition, Hsp90 knockdown abrogates colocalization of Hsp90 and HMGA2 in CRC cells. Moreover, the suppression of HMGA2 protein expression in response to NVP-AUY922 treatment resulted in ubiquitination and subsequent proteasome-dependant degradation of HMGA2. Furthermore, RNAi-mediated silencing of HMGA2 reduced the survival of CRC cells and increased the sensitivity of these cells to chemotherapy. Finally, we found that the NVP-AUY922-dependent mitigation of HMGA2 signaling occurred also through indirect reactivation of the tumor suppressor microRNA (miRNA), let-7a, or the inhibition of ERK-regulated HMGA2 involved in regulating the growth of CRC cells. Collectively, our studies identify the crucial role for the Hsp90-HMGA2 interaction in maintaining CRC cell survival and migration. These findings have significant implications for inhibition HMGA2-dependent tumorigenesis by clinically available Hsp90 inhibitors.

HPW-RX40 restores anoikis sensitivity of human breast cancer cells by inhibiting integrin/FAK signaling

Anoikis is defined as apoptosis, which is induced by inappropriate cell-matrix interactions. Cancer cells with anoikis resistance tend to undergo metastasis, and this phenomenon has been reported to be associated with integrin and FAK activity. HPW-RX40 is a derivative of 3,4-methylenedioxy-β-nitrostyrene, which is known to prevent platelet aggregation by inhibition of integrin. In the present study, we investigated the effect of HPW-RX40 on an anoikis-resistant human breast cancer cell line MDA-MB-231. HPW-RX40 inhibited cell aggregation and induced cell death in suspending MDA-MB-231 cells, but had only little effect on the monolayer growth of adherent cells. Analysis of caspase activation and poly (ADP-ribose) polymerase (PARP) cleavage confirmed anoikis in HPW-RX40-treated suspending cancer cells. HPW-RX40 also affected the Bcl-2 family proteins in detached cancer cells. Furthermore, HPW-RX40 inhibited detachment-induced activation of FAK and the downstream phosphorylation of Src and paxillin, but did not affect this pathway in adherent cancer cells. We also found that the expression and activation of β1 integrin in MDA-MB-231 cells were reduced by HPW-RX40. The combination of HPW-RX40 with an EGFR inhibitor led to enhanced anoikis and inhibition of the FAK pathway in breast cancer cells. Taken together, our results suggest that HPW-RX40 restores the anoikis sensitivity in the metastatic breast cancer cells by inhibiting integrin and subsequent FAK activation, and reveal a potential strategy for prevention of tumor metastasis.

Meaningful prevention of breast cancer metastasis: candidate therapeutics, preclinical validation, and clinical trial concerns

The development of drugs to treat breast and other cancers proceeds through phase I dose finding, phase II efficacy, and phase III comparative studies in the metastatic setting, only then asking if metastasis can be prevented in adjuvant trials. Compounds without overt cytotoxic activity, such as those developed to inhibit metastatic colonization, will likely fail to shrink established lesions in the metastatic setting and never be tested in a metastasis prevention scenario where they were preclinically validated. We and others have proposed phase II primary and secondary metastasis prevention studies to address this need. Herein, we have asked whether preclinical metastasis prevention data agrees with the positive adjuvant setting trials. The data are limited but complimentary. We also review fundamental pathways involved in metastasis, including Src, integrins, focal adhesion kinase (FAK), and fibrosis, for their clinical progress to date and potential for metastasis prevention. Issues of inadequate preclinical validation and clinical toxicity profiles are discussed.

Heat shock protein 90β stabilizes focal adhesion kinase and enhances cell migration and invasion in breast cancer cells

Focal adhesion kinase (FAK) acts as a regulator of cellular signaling and may promote cell spreading, motility, invasion and survival in malignancy. Elevated expression and activity of FAK frequently correlate with tumor cell metastasis and poor prognosis in breast cancer. However, the mechanisms by which the turnover of FAK is regulated remain elusive. Here we report that heat shock protein 90β (HSP90β) interacts with FAK and the middle domain (amino acids 233-620) of HSP90β is mainly responsible for this interaction. Furthermore, we found that HSP90β regulates FAK stability since HSP90β inhibitor 17-AAG triggers FAK ubiquitylation and subsequent proteasome-dependent degradation. Moreover, disrupted FAK-HSP90β interaction induced by 17-AAG contributes to attenuation of tumor cell growth, migration, and invasion. Together, our results reveal how HSP90β regulates FAK stability and identifies a potential therapeutic strategy to breast cancer.

Targeting FAK in human cancer: from finding to first clinical trials

It is twenty years since Focal Adhesion Kinase (FAK) was found to be overexpressed in many types of human cancer. FAK plays an important role in adhesion, spreading, motility, invasion, metastasis, survival, angiogenesis, and recently has been found to play an important role as well in epithelial to mesenchymal transition (EMT), cancer stem cells and tumor microenvironment. FAK has kinase-dependent and kinase independent scaffolding, cytoplasmic and nuclear functions. Several years ago FAK was proposed as a potential therapeutic target; the first clinical trials were just reported, and they supported further studies of FAK as a promising therapeutic target. This review discusses the main functions of FAK in cancer, and specifically focuses on recent novel findings on the role of FAK in cancer stem cells, microenvironment, epithelial-to-mesenchymal transition, invasion, metastasis, and also highlight new approaches of targeting FAK and critically discuss challenges that lie ahead for its targeted therapeutics. The review provides a summary of translational approaches of FAK-targeted and combination therapies and outline perspectives and future directions of FAK research.

High FAK combined with low JWA expression: clinical prognostic and predictive role for adjuvant fluorouracil-leucovorin-oxaliplatin treatment in resectable gastric cancer patients

BACKGROUND

The multifunctional protein JWA was previously identified as a novel regulator of focal adhesion kinase (FAK/PTK2) in suppressing cancer cell adhesion, invasion and metastasis. JWA is downregulated in gastric cancer (GC) and a prognostic and predictive biomarker for resectable GC. However, the value of FAK combined with JWA for GC patients as a biomarker has not been studied. Here we evaluated the roles of FAK alone and combined with JWA in GC patients treated with surgery alone or combined with adjuvant platinum-based chemotherapy.

METHODS

Two tissue microarrays were constructed of specimens from resected GC (n = 709 in total) for detection of FAK and JWA expression by immunohistochemistry. Correlations between both proteins and clinicopathological features as well as prognostic and predictive values were evaluated.

RESULTS

Compared with adjacent non-cancerous tissues, FAK protein levels were remarkably up-regulated in GC lesions (P < 0.001). High FAK alone or combined with low JWA expression significantly correlated with worse overall survival (OS) (both P < 0.001 in two cohorts). Simultaneously, JWA plus FAK expression was a more valuable prognostic biomarker than JWA or FAK alone. Moreover, the patients with high FAK only or combined with low JWA had significant benefit from adjuvant fluorouracil-leucovorin-oxaliplatin (FLO) therapy compared with those with surgery alone (P = 0.003); however, the cases with adjuvant fluorouracil-leucovorin-cisplatin (FLP) therapy did not show these effects.

CONCLUSION

FAK plus JWA may serve as a more prognostic and predictive biomarker for GC than each separately with a potential clinical application.

Stabilization of integrin-linked kinase by the Hsp90-CHIP axis impacts cellular force generation, migration and the fibrotic response

Integrin-linked kinase (ILK) is an adaptor protein required to establish and maintain the connection between integrins and the actin cytoskeleton. This linkage is essential for generating force between the extracellular matrix (ECM) and the cell during migration and matrix remodelling. The mechanisms by which ILK stability and turnover are regulated are unknown. Here we report that the E3 ligase CHIP-heat shock protein 90 (Hsp90) axis regulates ILK turnover in fibroblasts. The chaperone Hsp90 stabilizes ILK and facilitates the interaction of ILK with α-parvin. When Hsp90 activity is blocked, ILK is ubiquitinated by CHIP and degraded by the proteasome, resulting in impaired fibroblast migration and a dramatic reduction in the fibrotic response to bleomycin in mice. Together, our results uncover how Hsp90 regulates ILK stability and identify a potential therapeutic strategy to alleviate fibrotic diseases.

Structure-based discovery of cellular-active allosteric inhibitors of FAK

In order to develop potent and selective focal adhesion kinase (FAK) inhibitors, synthetic studies on pyrazolo[4,3-c][2,1]benzothiazines targeted for the FAK allosteric site were carried out. Based on the X-ray structural analysis of the co-crystal of the lead compound, 8-(4-ethylphenyl)-5-methyl-1,5-dihydropyrazolo[4,3-c][2,1]benzothiazine 4,4-dioxide 1 with FAK, we designed and prepared 1,5-dimethyl-1,5-dihydropyrazolo[4,3-c][2,1]benzothiazin derivatives which selectively inhibited kinase activity of FAK without affecting seven other kinases. The optimized compound, N-(4-tert-butylbenzyl)-1,5-dimethyl-1,5-dihydropyrazolo[4,3-c][2,1]benzothiazin-8-amine 4,4-dioxide 30 possessed significant FAK kinase inhibitory activities both in cell-free (IC50=0.64μM) and in cellular assays (IC50=7.1μM). These results clearly demonstrated a potential of FAK allosteric inhibitors as antitumor agents.

Vascular endothelial growth factor C enhances cervical cancer migration and invasion via activation of focal adhesion kinase

Vascular endothelial growth factor C (VEGF-C) is correlated positively with clinical cervical cancer metastasis and survival. Previously we showed that VEGF-C directly activated actin-binding protein moesin, leading to the formation of membrane protrusions. However, whether VEGF-C alters cervical cancer cell adhesion to the extra-cellular matrix is currently unknown. In this study, we investigated the effects of VEGF-C on the formation of focal adhesion complexes, which provide anchoring sites for cell attachment to the extracellular matrix. On cultured cervical carcinoma cell line SiHa cells, VEGF-C enhanced focal adhesion kinase (FAK) phosphorylation. As a result, VEGF-C led to increased formation of focal adhesion complexes and enhanced migration and invasion, which was reversed by siRNA abrogating FAK. VEGF-C resulted in increased interaction of its receptor Flt-4 with non-receptor tyrosine kinase c-Src, leading to c-Src phosphorylation. The specific inhibitor of c-Src kinase, PP2, or the transfection with specific c-Src siRNA largely impaired VEGF-C-enhanced FAK phosphorylation, suggesting that Flt-4/c-Src cascade plays a central role in these processes. These results implied that VEGF-C promotes cervical cancer metastasis by activation of FAK protein through Flt-4/c-Src pathway.

Orthotopic xenograft model of cervical cancer for studying microenvironmental effects on metastasis formation and response to drug treatment

Cancers arising in the uterine cervix are usually squamous cell carcinomas that develop from preneoplastic lesions. They invade locally, and then typically metastasize to the regional lymph nodes and eventually to distant sites. Orthotopically grown xenografts are technically challenging to perform, but recapitulate the clinical situation to a greater extent than xenografts grown at subcutaneous or intramuscular sites. Thus, orthotopic xenografts develop lymphovascular invasion and metastasize to the para-aortic lymphatic chain in a pattern similar to that seen in patients. The extent of (lymph node) metastases is particularly apparent when the implanted tumor cells are transfected to express a fluorescent marker, such as DsRed, which allows the exposed retroperitoneum to be examined by fluorescence microscopy. Described in this unit is a surgical technique for orthotopic implantation and the use of this model for investigating the effects of novel agents as inhibitors of tumor growth and metastasis.

Optical imaging with her2-targeted affibody molecules can monitor hsp90 treatment response in a breast cancer xenograft mouse model

PURPOSE

To determine whether optical imaging can be used for in vivo therapy response monitoring as an alternative to radionuclide techniques. For this, we evaluated the known Her2 response to 17-dimethylaminoethylamino-17-demethoxygeldanamycin hydrochloride (17-DMAG) treatment, an Hsp90 inhibitor.

EXPERIMENTAL DESIGN

After in vitro 17-DMAG treatment response evaluation of MCF7 parental cells and 2 HER2-transfected clones (clone A medium, B high Her2 expression), we established human breast cancer xenografts in nude mice (only parental and clone B) for in vivo evaluation. Mice received 120 mg/kg of 17-DMAG in 4 doses at 12-hour intervals intraperitonially (n = 14) or PBS as carrier control (n = 9). Optical images were obtained both pretreatment (day 0) and posttreatment (day 3, 6, and 9), always 5 hours postinjection of 500 pmol of anti-Her2 Affibody-AlexaFluor680 via tail vein (with preinjection background subtraction). Days 3 and 9 in vivo optical imaging signal was further correlated with ex vivo Her2 levels by Western blot after sacrifice.

RESULTS

Her2 expression decreased with 17-DMAG dose in vitro. In vivo optical imaging signal was reduced by 22.5% in clone B (P = 0.003) and by 9% in MCF7 parental tumors (P = 0.23) 3 days after 17-DMAG treatment; optical imaging signal recovered in both tumor types at days 6 to 9. In the carrier group, no signal reduction was observed. Pearson correlation of in vivo optical imaging signal with ex vivo Her2 levels ranged from 0.73 to 0.89.

CONCLUSIONS

Optical imaging with an affibody can be used to noninvasively monitor changes in Her2 expression in vivo as a response to treatment with an Hsp90 inhibitor, with results similar to response measurements in positron emission tomography imaging studies.

The role of focal adhesion kinase catalytic activity on the proliferation and migration of squamous cell carcinoma cells

Focal adhesion kinase (FAK) is upregulated in several epithelial tumours and there has been considerable interest in developing small molecule kinase inhibitors of FAK. However, FAK also has important adaptor functions within the cell, integrating signals from both integrins and growth factors. To investigate the role of FAKs kinase domain, we generated fak-deficient squamous cell carcinoma (SCC) cell lines. Re-expression of a wild type or kinase dead FAK allowed us to delineate its kinase dependent functions. In addition, we used the novel FAK kinase inhibitor PF-562,271. The kinase activity of FAK was important for tumour cell migration and polarity but more striking was its requirement for the anchorage independent 3 dimensional (3D) proliferation of SCC cells and their growth as xenografts in mice. Inhibition of FAK activity and prevention of growth in 3D correlated with Src inhibition. We further identified a mechanism whereby FAK regulates proliferation in 3D via regulation of the kinase activity of Src. This was dependent on the kinase activity of FAK and its resulting phosphorylation on Y397 that provides a high affinity binding site for Src. These data support the further development of FAK kinase inhibitors as agents that have the potential to inhibit both tumour cell migration and proliferation.

Dual targeting of EGFR and focal adhesion kinase in 3D grown HNSCC cell cultures

PURPOSE

Epidermal growth factor receptor (EGFR) and focal adhesion kinase (FAK) show frequent overexpression and hyperactivity in various human malignancies including head and neck squamous cell carcinomas (HNSCC). To examine effects of dual EGFR/FAK inhibition on cellular radiosensitivity of HNSCC cells in a more physiological environment, we employed a previously established laminin-rich extracellular matrix (lrECM) based three-dimensional (3D) cell culture model.

MATERIALS AND METHODS

UTSCC15 and SAS HNSCC cell lines stably transfected with EGFR-CFP or CFP were used. Single or combined EGFR (Cetuximab, siRNA) and FAK (TAE226, siRNA) inhibition were accomplished prior to measuring clonogenic survival and protein expression and phosphorylation. Immunofluorescence enabled visualization of EGFR-CFP and FAK.

RESULTS

Cetuximab resulted in higher radiosensitization in EGFR-CFP overexpressing cell lines than CFP controls. Single EGFR or FAK inhibition mediated radiosensitization, while dual EGFR/FAK targeting further augmented this effect. Despite signaling alterations upon Cetuximab and siRNA knockdown, analysis of protein expression and phosphorylation indicates EGFR and FAK signaling coexistence without obvious overlap.

CONCLUSIONS

Combined EGFR/FAK targeting yielded stronger radiosensitization than either approach alone, which might be based on non-overlapping downstream signaling. Whether dual targeting of EGFR and FAK can reasonably be combined with radiotherapy and chemotherapy needs clarification.

Therapeutic targeting of tumor-stroma interactions

INTRODUCTION

Cancers exist within a complex microenvironment populated by diverse cell types within a protein-rich extracellular matrix. It is becoming increasingly apparent that molecular interactions between epithelial cells and cells in the surrounding stroma promote growth, invasion and spread of the tumor itself and thus represents a crucial underlying driving force in tumorigenesis.

AREAS COVERED

This article reviews how key interactions between tumor epithelial cells and surrounding mesenchymal and immune cells can promote tumor progression and highlights molecular elements that might represent novel therapeutic targets.

EXPERT OPINION

The tumor microenvironment is increasingly being viewed as a potential therapeutic target with a number of strategies being developed to disrupt tumor-stroma interactions, in order to delay or circumvent tumor progression. Targeting elements of the tumor microenvironment, or signaling pathways in tumor cells activated as a consequence of stromal interactions, may prove a useful therapeutic strategy to prevent tumor development and progression. However, given the tumor cells' ability to circumvent various therapeutic agents when given as monotherapy, the success of these agents is likely to be seen when used in combination with existing treatments.

Anoikis mediators in oral squamous cell carcinoma

Anoikis - apoptotic cell death triggered by loss of extracellular matrix (ECM) contacts - is dysregulated in many chronic debilitating and fatal diseases. Mechanisms rendering tumor cells resistant to anoikis, although not completely understood, possess significant therapeutic promise. In death receptor-mediated anoikis mechanisms, focal adhesion kinase (FAK) and receptor-interacting protein (RIP) dissociate, leading to association of RIP with Fas, formation of the death-inducing signaling complex (DISC), activation of caspase-3, and propagation of anoikis. In contrast, anoikis resistance is accomplished through constitutive activation of survival pathways that include integrin-dependent activation of FAK and extracellular-signal-regulated kinase (ERK). In addition, FAK and RIP association confers anoikis resistance by inhibiting the association of RIP with Fas and formation of the death signaling complex, which allows cells to escape anoikis. Up-regulation of CD44 also contributes to survival signals and promotes anoikis resistance. This review will focus on the roles of death receptors, prosurvival pathways, and the molecular players involved in anoikis escalation and resistance in oral squamous cell carcinoma.

Therapeutic potential and limitations of new FAK inhibitors in the treatment of cancer

IMPORTANCE OF THE FIELD

Activation of the non-receptor tyrosine kinase focal adhesion kinase (FAK) has been implicated in progression of multiple mesenchymal and epithelial malignant tumors. FAK plays an important role in regulation of proliferation, migration and apoptosis of neoplastic cells.

AREAS COVERED IN THIS REVIEW

We review the importance of FAK expression as a prognostic marker in cancer patients, discuss the available small-molecule inhibitors of FAK, summarize the available data from early-phase clinical trials with FAK inhibitors and cover the antiangiogenic properties of FAK inhibitors, as well as their potential to overcome chemoresistance.

WHAT THE READER WILL GAIN

This review enables the reader to overview current knowledge about FAK inhibition in cancer therapy and its role in the clinical setting. The reader will be able to consider FAK inhibitors not only as direct antitumor but also as antineoangiogenic agents and drugs that can overcome the problem of chemoresistance.

TAKE HOME MESSAGE

Emerging data from early-phase clinical trials with orally available small-molecule inhibitors of FAK are promising. There are early indicators of clinical efficacy. In the future, combination therapy with cytotoxic or antiangiogenic drugs may help to overcome chemoresistance and enhance efficacy of antivascular therapy.

Targeting focal adhesion kinase signaling in tumor growth and metastasis

IMPORTANCE OF THE FIELD

Focal adhesion kinase (FAK), a crucial mediator of integrin and growth factor signaling, is a novel and promising target in cancer therapy. FAK resides within focal adhesions which are contact points between extracellular matrix (ECM) and cytoskeleton, and increased expression of the kinase has been linked with cancer cell migration, proliferation and survival. The aim of this review is to summarize the current research in the area and to assess the potential of different FAK-targeting strategies for cancer therapy.

AREAS COVERED IN THIS REVIEW

We briefly examine the evidence pointing towards FAK as potential anti-cancer target since its discovery in 1992. Then, we summarize different approaches developed to interfere with FAK signaling and important results reported from these experiments. Finally, we discuss the potential of these strategies to accomplish inhibition of tumor growth and distant spread as well as potentially meaningful combinations with other therapeutic modalities in the context of the currently available evidence.

WHAT THE READER WILL GAIN

The review emphasizes the link between FAK biology and the consequences of interference with FAK signaling. Based on this foundation an opinion is formed with regard to the future of FAK as therapeutic target.

TAKE HOME MESSAGE

Inhibition of FAK harbours the potential to restrain malignant growth and progression with minimal side effects in normal tissues. Small molecule inhibitors of the kinase should be examined in further clinical studies and combinations with existing therapies need to be explored. More efforts are required to identify markers which predict response towards FAK inhibition.

SNAI1 expression and the mesenchymal phenotype: an immunohistochemical study performed on 46 cases of oral squamous cell carcinoma

Background

SNAI1 can initiate epithelial-mesenchymal transition (EMT), leading to loss of epithelial characteristics and, in cancer, to invasion and metastasis. We hypothesized that SNAI1 reactivation occurs in oral squamous cell carcinoma (OSCC) where it might also be associated with focal adhesion kinase (FAK) expression and p63 loss.

Methods

Immunohistochemistry was performed on 46 tumors and 26 corresponding lymph node metastases. Full tissue sections were examined to account for rare and focal expression. Clinical outcome data were collected and analyzed.

Results

SNAI1-positivity (nuclear, ≥ 5% tumor cells) was observed in 10 tumors and 5 metastases (n = 12 patients). Individual SNAI1(+) tumor cells were seen in primary tumors of 30 patients. High level SNAI1 expression (>10% tumor cells) was rare, but significantly associated with poor outcome. Two cases displayed a sarcomatoid component as part of the primary tumor with SNAI1(+)/FAK(+)/E-cadherin(-)/p63(-) phenotype, but disparate phenotypes in corresponding metastases. All cases had variable SNAI1(+) stroma. A mesenchymal-like immunoprofile in primary tumors characterized by E-cadherin loss (n = 29, 63%) or high cytoplasmic FAK expression (n = 10, 22%) was associated with N(+) status and tumor recurrence/new primary, respectively.

Conclusions

SNAI1 is expressed, although at low levels, in a substantial proportion of OSCC. High levels of SNAI1 may herald a poor prognosis and circumscribed SNAI1 expression can indicate the presence of a sarcomatoid component. Absence of p63 in this context does not exclude squamous tumor origin. Additional EMT inducers may contribute to a mesenchymal-like phenotype and OSCC progression.